1. Field of the Invention
The present invention relates to phosphor blend for wavelength conversion, and more particularly, to phosphor blend for wavelength conversion capable of expressing a variety of colors, and further having a superior Color Rendering Index (CRI), which enables provision of white light that is close to natural light, and a white light emitting device using the same.
2. Description of the Related Art
In general, a phosphor for wavelength conversion is used for converting a specific wavelength light of diverse light sources into a desired wavelength light. Among the diverse light sources, since the LED is useful for LCD backlights, and for automobile and home illumination because of its low-power driving and superior light efficiency, the phosphor has become popular these days as technology essential in the manufacture of white light LEDs.
A white light emitting device is manufactured by applying a yellow phosphor on a blue LED. More specifically, a yellow phosphor YAG (Y3Al5O12):Ce is applied on a light emission surface of a blue LED having a GaN/InGaN active layer to convert parts of blue light into yellow light, and the converted yellow light and other parts of blue light are combined to provide white light.
The conventional white light emitting device composed of a YAG:Ce phosphor (or TAG-based phosphor) and a blue LED has a drawback of low color rendering quality. That is, the wavelength of white light obtained using the yellow phosphor is distributed only in blue and yellow regions, and its color rendering quality is low, and therefore, it is limited in realizing desired all-natural white light. In addition, if the operating temperature rises due to long use, the problematic yellowing occurs.
The conventional phosphor for wavelength conversion is limited only to provision of light emission colors of a specific light source and colors of specific output light, and also limited in achievable color distribution. Thus there are limitations in applying the conventional phosphor to light emission colors of diverse light sources and/or colors of diverse kinds of output light depending on the user's needs.
In order to reduce such problems, the assignee of this invention has previously proposed phosphor blend composed of blue, green, and red in Korean Patent Application No. 2004-0076300 (filed on Sep. 23, 2004).
As described above, there has been a need for phosphor blend which can mitigate yellowing and has superior Color Rendering Index at the same time, and further can achieve a broader color distribution in the art.